8.PS..2.1-Electric , Magnetic, and Gravitational Force

Magnetic and Electric Forces

Motion, Forces, Electricity & Magnetism

by Cecily Vaulx

Electricity and Magnetism

Test Review

What is a Magnet?

• Magnets are any material that attracts iron and materials that contain iron

• Magnets attract or repel other magnets

• One end of a magnet will always point north when allowed to swing freely

Multiple Choice

How do Magnetic Poles Interact?

• All magnets have two ends called magnetic poles

• The pole of the magnet that points north is called the north pole. The one that points south is the south pole.

• Unlike Poles attract

• Similar poles repel

• The poles have the strongest magnetic effect

Multiple Select

Select the two variables that determine the gravitational force between two objects

• mass

• volume

• magnetism

• distance

Multiple Choice

One student rubs a balloon against his hair several times. Another student passes a comb through her hair several times. The students place the comb near the balloon and observe that the comb repels the balloon. Which is the most likely reason the comb is able to repel the balloon?

• The balloon has a positive charge and the comb is neutral.

• The balloon and the comb have the same electrical charge.

• The balloon has a negative charge and the comb is neutral.

• The balloon and the comb have opposite electrical charges.

Multiple Choice

• The electrons will pass to the foam cup but will remain in a localized, positively charged area on the cup where the rod was placed.

• The electrons will pass to the foam cup but will remain in a localized, negatively charged area on the cup where the rod was placed.

• The electrons will pass from the foam cup to the aluminum can, and both the foam cup and the aluminum can will become positively charged.

• The electrons will pass from the foam cup to the aluminum can, and both the foam cup and the aluminum can will become negatively charged

Multiple Choice

A positive charge and a positive charge will _______.

• Attract 
• Repel

Multiple Choice

Which statement correctly describes the factors affecting gravitational force between two objects?

• Gravitational force between two objects is determined by their masses and the distance between their outermost edges

• Gravitational force between two objects is determined by their masses and the distance between their centers.

• Gravitational force between two objects is determined by their volumes and their acceleration relative to the Sun.

• Gravitational force between two objects is determined by their diameters and their distance from the Sun.

Multiple Choice

The Sun is the center of our solar system, which includes planets, dwarf planets, asteroids, and comets. Which statement best explains why all objects, including planets, orbit the Sun, instead of the Sun orbiting one or more planets?

• Planets have less mass than the Sun.

• The Sun rotates faster than any of the planets.

• The Sun formed before the planets or other objects.

• Planets are further from the center of the solar system.

Multiple Choice

A negative charge and a positive charge will ________.

• Attract
• Repel

Multiple Choice

A student attaches a rope to the handle of a chest loaded with a few books, while the other end of the rope is tied to a spring scale. The student pulls the scale with just enough force to set the chest in motion and records the force applied on the spring scale. The student repeats the experiment with more books in the chest and records the data in a table.

What can be concluded from the data?

• As the mass of the chest increases, less force is required to pull it.

• As the mass of the chest increases, more force is required to pull it.

• The amount of frictional force increases as the mass of the chest decreases.

• The amount of frictional force decreases as the mass of the chest increases.

Multiple Choice

The part of the magnet with the strongest attraction and is labeled N and S is called magnetic __________.

• poles 
• attractor
• repel
• compass

Multiple Choice

What is produced by a stream of electrons flowing through a wire that is coiled around an iron core?

• an atomic field

• a radiation field

• a magnetic field

• a static field

Multiple Choice

Any material that exerts magnetic force is considered a magnet

• True

• False

Multiple Choice

A student claims that Earth has a magnetic field. Which evidence would best support the student's claim?

• The student creates a working circuit that illuminates a bulb using wire and a battery.

• The student turns in all directions with a compass and the needle always points north.

• The student receives a shock after walking across the carpet and touching a doorknob.

• The student rolls a ball down a large hill and the ball comes to a complete stop at the bottom.

Multiple Choice

A student builds an electromagnet, as shown.

Will the compass needle move when brought near the electromagnet, and why?

• Yes. The needle of a compass changes direction randomly when brought near the electromagnet.

• No. The needle of a compass will not react because the wires are not connected to the battery properly in order to create a working electromagnet.

• No. The needle of a compass only aligns itself with an electric field, which cannot be created by the electromagnet.

• Yes. The needle of a compass aligns itself with the magnetic field created by the electromagnet.

Multiple Choice

Like all other forces, a magnetic force is a(n) gravitational force

• True

• False it is actually a push or pull

• False it is actually a Potential Force

Multiple Choice

A group of students plans to make a small compass using a blunt sewing needle. What is the next step they should perform with the needle?

• press it between two hard surfaces

• heat it on a candle flame

• rub it on a bar magnet

• scratch it on a steel spoon

Multiple Choice

The diagram shows a firefighter operating a hose. The arrows show the forces acting on the hose.

Which statement describes the situation in the diagram?

• Since the firefighter is at rest, he does not move as he operates the hose.

• The hose has very little friction, making it slide toward the firefighter.

• The firefighter's mass decreases the force of the water escaping from the hose.

• The water escaping from the hose exerts an equal and opposite force on the hose.

Multiple Choice

When freely swinging, one end of the magnet always points east

• True

• False, it points north

• False it points west

• False it points randomly

Multiple Choice

Which statement about conductors and insulators charging is correct?

• Both conductors and insulators charge through friction.

• Both conductors and insulators charge through induction.

• Conductors charge through induction, whereas insulators charge through friction.

• Conductors charge through friction, whereas insulators charge through induction.

Multiple Choice

When a hammer strikes a nail, the nail

• exerts balanced forces that helps it from moving.

• exerts a force equal to the weight of the hammer.

• exerts an unbalanced force that changes its velocity.

• exerts an equal and opposite force back on the hammer.

Multiple Choice

• The balloons will hang at a greater elevation, because they will have greater charges so the force of electrical repulsion between them will be greater.

• The balloons will hang at a smaller elevation, because more thoroughly rubbing them will more completely remove their charges, reducing the electrical repulsion between them.

• The balloons will hang at the same elevation, because electrical repulsion is an unvarying phenomenon which results from the existence of charge and not its quantity.

• The balloons will hang straight down or more closely together, because a larger number of rubs with fur will give them opposite rather than like electrical charges.

What is a Magnetic Field's Shape?

• Magnetic force is strongest at the poles but not limited to the poles

• The area of magnetic force around a magnet is known as its magnetic field

• Because of magnetic fields, magnets can interact without even touching

Multiple Choice

Use the scenario to answer the question.

Activity 1 Gia pushes two toy cars (1 and 2), each with a different mass, with the same amount of force in the same direction and records the time it takes for each toy car to move two meters, as shown in the table.

Activity 2 Shamiyah pushes Toy Car 1 from two opposite directions at the same time in several trials, as shown.

• Trial 1

• Trial 2

• Trial 3

• Trial 4

Multiple Choice

• They move to the top of both cans.

• They move to the bottom in both cans.

• They move from the right can to the left can.

• They move from the left can to the right can.

• Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole

• Magnetic field lines will always leave the north pole and enter the south pole

• The closer the lines are, the stronger the field

• Magnetic field lines are closest together at the poles

Multiple Choice

• Balloon 1, only

• Plastic sheet 1, only

• Balloon 1 and Plastic sheet 2

• Balloon 2 and Plastic sheet 1

Multiple Choice

Cyniah walked the route marked in the diagram from her home at point J to point O.

When Cyniah reaches point O, what is her new position relative to her home at point J?

• 20 meters north

• 25 meters north

• 60 meters north

• 70 meters north

Multiple Choice

• It will distribute itself evenly over the surface of the sphere, because like charges repel and the sphere is a conductor.

• It will remain at the point of contact between the rod and the sphere, because resistance in the metal prevents the charges from easily moving.

• It will quickly spread to the air around the sphere, because it will seek to occupy as large a volume of neutral matter as possible.

• It will slowly drift to the bottom of the sphere, because the charges rapidly attach to individual atoms, making them slightly heavier than surrounding atoms.

What is Earth's Magnetic Field Like?

• A compass is a device that has a magnet on a needle that spins freely. The needle points north.

• Just like a bar magnet, Earth has a magnetic field around it and two magnetic poles.

• The poles of a magnetized compass needle align with Earth's magnetic Field

• 
  

Earth's Core

• Earth's core is a large sphere of metal at Earth's center

• The outer core is made of hot swirling liquid iron

• The motion of this iron creates a magnetic field similar to the magnetic field of a bar magnet

• 
  

Multiple Choice

• She should place a negatively charged rod near the left sphere.

• She should place a positively charged rod near the left sphere.

• She should place two negatively charged rods near each sphere.

• She should place two positively charged rods near each sphere.

Multiple Choice

A student performs an activity using a sheet of paper, a magnet, and a steel ball. The image shows the setup.

The student observes that the steel ball sticks to the magnet even though the paper is between them. Which factor leads to the attraction of the ball to the magnet?

• The magnet exerts a force on the ball.

• The magnet attracts the paper, which pulls the ball.

• The paper exerts a force on the ball, which pulls the ball toward the magnet.

• The size of the ball attracts the ball toward the magnet.

Multiple Choice

When a plastic rod is rubbed with a wool cloth, the wool acquires a positive charge. What is the best explanation for this effect?

• protons are transferred to the cloth

• protons are transferred to the rod

• electrons are transferred to the cloth

• electrons are transferred to the rod

Multiple Choice

Magnetic field lines are closest together...

• near the center of the magnet

• At the magnet's poles

• North pole only

• South pole only

Multiple Choice

Jazzy designs two electromagnets of different strengths. The first electromagnet has an insulated copper wire wrapped around an iron nail many times before it is connected to a battery. The second electromagnet has its insulated copper wire wrapped around a similar nail a fewer number of times before it is connected to two smaller batteries as shown in the image.

Jazzy tries to determine which electromagnet is stronger by bringing each near a bowl containing eight metal paper clips. She observes that both electromagnets attract all eight of the paper clips.

How can Jazzy demonstrate that each electromagnet has a different strength?

• Place a metal paper clip on a table and slowly bring each electromagnet closer to the paper clip to see which can attract the paper clip from a greater distance.

• Determine which electromagnet has its copper wire wrapped around its iron nail a greater number of times.

• Add plastic paper clips to the bowl and check which electromagnet can attract both kinds of paper clips.

• Reduce the number of paper clips in the bowl and find which electromagnet attracts more paper clips.

  Reduce the number of paper clips in the bowl and find which electromagnet attracts more paper clips.

Multiple Choice

Markeisha needs to create an electromagnet for her science project. She needs to create a magnet that can pick up iron filings out of a mixture of substances. Which list of materials would best help Markeisha build her electromagnet?

• string, battery, metal nail

• battery, metal nail, wire

• glass rod, wire, battery

• glass rod, string, battery

Multiple Choice

A _________ is a particle with a positive charge.

• Neutron
• Electron
• Proton

Multiple Choice

A 100 kg box is initially at rest on a level surface. One 10 N force acts on the box, directed toward the right. A second 10 N force acts simultaneously on the box, directed toward the left, as shown.

How is the box affected by the two forces?

• The box will move because unbalanced forces are acting on it.

• The box will move because balanced forces are acting on it.

• The box will not move because unbalanced forces are acting on it.

• The box will not move because balanced forces are acting on it.

Multiple Choice

• It will distribute itself evenly over the surface of the sphere, because like charges repel and the sphere is a conductor.

• It will remain at the point of contact between the rod and the sphere, because resistance in the metal prevents the charges from easily moving.

• It will quickly spread to the air around the sphere, because it will seek to occupy as large a volume of neutral matter as possible.

• It will slowly drift to the bottom of the sphere, because the charges rapidly attach to individual atoms, making them slightly heavier than surrounding atoms.

Multiple Choice

This tool is a ___________.

• Compass
• Pole
• Star
• GPS

Multiple Choice

What is the transfer of energy in a generator?

• electrical to mechanical

• chemical to radiant

• electrical to chemical

• mechanical to electrical

Electromagnetic Force

• Magnets have magnetic fields...BUT an electric current can also produce a magnetic field!

• Whenever there is electricity, there is magnetism

• An electric current produces a magnetic field

• This relationship is called electromagnetism

Multiple Choice

Four smooth blocks are being pushed along a smooth surface. The diagram shows the mass of the blocks and the force applied to each block.

What can be concluded about the motion of the blocks?

• Block 1 will move the farthest.

• Block 1 will move farther than Block 3.

• Blocks 2 and 3 will not move.

• Block 4 will move farther than Block 2.

Electric Current

• The circuit must be closed for electric current to flow

• If the circuit is open, the current cannot flow

• 
  

• 
  

Multiple Choice

A student wraps insulated copper wire 12 times around a nail, and connects the ends to a fresh 9-volt battery. The student finds that the nail can now be used to lift small iron weights. The student disconnects the circuit and wraps a longer copper wire 30 times around another nail of the same type. The student then connects the wire to a fresh 9-volt battery. What should the student observe when attempting to use the new nail to lift small iron weights?

• The nail will be able to lift heavier weights, because the greater number of turns of the wire yields a more powerful magnetic field.

• The nail will be able to lift heavier weights, because the greater mass of conductive matter in the system will balance a greater mass of iron in the weights.

• The nail will only be able to lift the same amount of weight, because the magnetic force of the system depends on the current from the battery, which has not changed.

• The nail will only be able to lift the same amount of weight, because the physical properties of the nail determine magnetic force, and nails of the same type were used in both trials.

Multiple Choice

Would increasing the number of batteries in a circuit that is connected to a small electric motor affect the speed of the motor, if all other variables are kept constant?

• No, because it is the magnetic force, not the electric force, that controls the motor speed.

• Yes, the motor would run faster because the increased electrical force increases the magnetic force in the motor.

• No, the speed of a motor is controlled only by the number of wire coils in the motor.

• Yes, the motor would run faster because increased current causes the motor to become warmer.

Multiple Choice

Seamus made an electromagnet from an iron nail, a piece of copper wire with three coils spread out across the nail, and a AAA-sized battery. His magnet attracts only one paper clip, and he wants to boost the power of his magnet to attract at least four paper clips. What two things can Seamus do to accomplish his goal?

• Seamus can add batteries to decrease the voltage, and he can decrease the space between the wire coils.

• Seamus can add batteries to increase the voltage, and he can increase the space between the wire coils.

• Seamus can add batteries to increase the voltage, and he can decrease the space between the wire coils.

• Seamus can add batteries to decrease the voltage, and he can increase the space between the wire coils.

What is a Magnetic Field Produced by a Current Like?

• The magnetic field produced by a current has a strength and a direction.

• The field can be turned on or off, have its direction reversed, or have its strength changed

Multiple Choice

Brielle tests the difference in the magnetic force of two electromagnets with different numbers of wire turns around the iron nails. She observes that the electromagnet with ten wire turns attracts more paper clips than the electromagnet with seven wire turns. What is her conclusion?

• Magnetic force increases with an increase in the number of wire turns around an iron nail.

• Magnetic force decreases with an increase in the number of wire turns around an iron nail.

• Magnetic force increases with a decrease in the number of wire turns around an iron nail.

• Magnetic force is not affected by a change in the number of wire turns around an iron nail.

Multiple Choice

Tony is playing with his toy car. A parachute in the back of the car is released to help slow down the car.

If the forces act on the car as shown in the picture, what is the net force?

Multiple Choice

What results from a wire carrying a current?

• an electric field

• a magnetic field

• beams of white light

• the dispersion of photons

Change the Strength of a Magnetic Field

• Increase the amount of current in the wire (battery strength)

• Increase your loops in your wire!

• The magnetic field around the wire forms a CIRCLE. When you make a loop in a wire, this causes the magnetic field lines to bunch closer together

• Magnetic forces increase when magnetic field lines are closer together

Multiple Choice

A machine is designed to test the strength of windows. The machine exerts a force on a window, as shown in the diagram.

The window does not break. Which is the correct force diagram that represents the scenario?

Multiple Choice

Two new planets are discovered, planet X and planet Y. The planets have identical volumes, but the mass of planet X is two times greater than the mass of planet Y. If two identical space ships land on each planet, which of the following will be true?

• The mass of the space ship on planet Y will be greater than the mass of the space ship on planet X.

• The weight of the space ship on planet Y will be greater than the weight of the space ship on planet X.

• The mass of the space ship on planet X will be greater than the mass of the space ship on planet Y.

• The weight of the space ship on planet X will be greater than the weight of the space ship on planet Y.

Multiple Choice

When electrons flow through wires from a - terminal to a + terminal a/an ___________ is created.

• Flow

• Electromagnet

• Current

• Magnet

Multiple Choice

A student hangs a pith ball from a stand using thread and rubs a glass rod with a silk cloth. Upon bringing the glass rod near the pith ball, the student observes that the pith ball is attracted toward the glass rod, as shown.

How can the observation best be explained?

• The glass rod exerts a gravitational force, causing it to attract the pith ball.

• The pith ball exerts a repulsion force toward the glass rod, causing the attraction.

• An electric field exists between the glass rod and the pith ball, causing the attraction.

• Electric charges in the string transfer to the pith ball, causing it to attract the glass rod.

Multiple Choice

Harper touches a negatively charged plastic rod to a rubber ball. How are the negative charges distributed on the rubber ball?

• They move to the bottom surface of the ball.

• They are evenly distributed on the inside of the ball.

• They are evenly distributed on the surface of the ball.

• They stay on the surface where the rod touches the ball.

Multiple Choice

The magnetic field of a magnet is ____________ further away from the magnet.

• Smaller

• Stroner

• Larger

• Weaker

Multiple Choice

Ahmad made a very simple electromagnet out of a nail, copper wire, and a AAA-sized battery. His magnet was able to lift one paper clip from 2 centimeters away. Which of the following is NOT a way Ahmad can improve the strength of his electromagnet?

• He can reverse the orientation of his battery

• He can use a thicker piece of the copper wire.

• He can increase the size and voltage of his battery.

• He can use longer wire for more coils around the nail.

Multiple Choice

What forces works only by combining electric and magnetic forces?

• electric

• magnetic

• static electricity

• electromagnet

Multiple Choice

Jazelle has five different-sized magnets. She puts each magnet far away from a paper clip and slowly moves it closer until it attracts the paper clip. She records the distance between the magnet and the paper clip when it attracts. What is Jazelle's experiment designed to test?

• how the size of a magnet affects the strength of its magnetic pull on objects

• how the type of paper clip affects the way in which it reacts to the force of a magnet

• how the distance away from a magnet affects a paper clip's chances of being attracted

• how the magnetic force of a magnet affects the movement of an object

Multiple Choice

The battery is the ________ of energy.

• Wire 
• Source 
• Insulator
• Negative

Multiple Choice

Kayla has two magnets. She would like to know how much magnetic energy is stored in each one. What would be the best way for her to determine which magnet has the most magnetic energy?

• Attach wires to the ends of each magnet and measure the currents going through the wires.

• Put each magnet into a beaker of water to see how much water it displaces.

• Measure how close each 0magnet can get to a metal object before picking it up.

• Record the mass of each magnet by measuring it on a balance scale

Multiple Choice

Is this an open circuit or a closed circuit?

• Open 
• Closed

Multiple Choice

Which type of electromagnetic core will create the strongest magnetic field?

• another magnet

• a wooden pencil

• an iron nail

• a glass rod

Multiple Choice

Is this an open circuit or a closed circuit?

• Open 
• Close

FINAL BRAIN BREAK

Multiple Choice

Which object could replace the penny and the light bulb would still light up?

• Crayon
• Toothpick
• Rubberband
• Paperclip

Multiple Choice

An electric ________ produces a magnetic field.

• Battery

• Magnet

• Current

• Circuit